1. Field of the Invention
This invention relates to flame retardant latex coatings, and particularly to coatings prepared from compositions such as dibromostyrene-butadiene and dibromostyrene-styrene-butadiene latices.
2. Description of the Prior Art
Styrene based copolymers and terpolymers have found many applications in the prior art. Styrene-butadiene rubbers (SBR) containing low styrene proportions (15%-35%) have been used for many applications, including tires, retreading, belting, footwear, wire and cable coating, sponge rubber, pressure-sensitive tape, reinforcement plastics and easy-processing polymers. Styrene-butadiene resins containing high percentages of styrene (60%-83%) have been used as reinforcing resins and coating resins. Styrene-butadiene latices containing varying amounts of styrene (15%-65%) have been used in fabric-to-rubber adhesives, foamed carpet backing, textile adhesives and carpet laminating. Crosslinked and non-crosslinked SBR polymers composed of 5%-43% styrene have been used as adhesives and sealants.
Although such styrene based compounds have had wide usage, there has remained a need to prepare styrene polymers having better flame retardant properties. The usual method by which flame-retarding properties are imparted to plastics is the blending-in of flame retardants. Many of the commonly used flame retardants contain bromine, for example brominated diphenyl or diphenyloxide compounds, together with antimony trioxide. These flame retardants impart good flame-retarding properties when included in the plastics mixture by blending.
However, these flame retardants have a major disadvantage in that the processing of plastics incorporating brominated flame retardants can give rise to problems. For example, the flame retardant or decomposition products thereof may be released during processing. This can cause an offensive odor, and in certain cases noxious compounds may be released. In addition, these flame retardants may significantly affect the mechanical properties of the plastics in which they are contained.
Many proposals have been made to overcome such difficulties. A number of proposals simply amount to the replacement of the brominated compounds with compounds containing nitrogen and/or phosphorus, which compounds are similarly blended into the plastic. Although these compounds may present fewer problems in processing than the bromine-containing flame retardants, for the most part they also have the disadvantage of adversely influencing the mechanical properties of the plastics.
Nae, "New Epoxy Resins Based on Bromostyrene-Butadiene Cotelomers", Polymer Prep., V.27(2), p. 399-400 (1986), described the synthesis of a limited class of epoxy resins based on the preparation of cotelomers which were subsequently epoxidized. Hydrogen peroxide was used as both the initiator and the telogen for the reaction of bromostyrene (mono, di and tri) with 1,3-butadiene to yield cotelomers having terminal--OH groups. The cotelomers were semi-liquids or solids, with molecular weights ranging from 1,000 to 14,000. These random oligomers were then epoxidized to produce epoxy resins useful as a matrix for composite materials. In U.K. Patent Application GB 2,164,051A published on Mar. 12, 1986, Nae, et al. claimed the same OH-terminated cotelomers having molecular weights of 600 to about 14,000. These cotelomers were described as being useful components of flame retardant polymers, especially polyurethanes.
In Canadian Patent No. 907,229, issued on Aug. 8, 1972, Mackay described a latex of a carboxylic acid based polymer. In addition to an .alpha.,.beta.-ethylenically unsaturated carboxylic acid monomer or a compound hydrolyzable to such a carboxylic acid monomer, the polymers comprised a ring-halogenated ethylenically unsaturated aromatic monomer (e.g., monochlorostyrene) and an aliphatic conjugated diene (e.g., butadiene). Mackay indicated that the practice of his invention in preparing fire-resistant latex foam required a carboxylic acid, a melamine-formaldehyde resin, antimony trioxide and a filler comprising an amphoteric metal oxide hydrate. Neither a copolymer of the class of dibromostyrene-butadiene, nor a terpolymer such as dibromostyrene-styrene-butadiene was discussed. Mackay did disclose that a small amount of styrene could be used along with the above prescribed monomers in the copolymer, and indicated in one example that 2,4-dibromostyrene as a monomer was used to prepare a carboxylic latex containing acrylic acid, dibromostyrene and 1,3-butadiene.